Here's a rundown of the rumor consensus, although very, very few details are known for sure. One of the few is that both new tablets will be running the redesigned iOS 7.

Thinner and lighter 9.7-inch iPad

Apple is expected to change the display technology for the big iPad's high resolution screen, adopting technologies it introduced with iPad mini. Instead of two glass sheets, one sheet will be replaced with a film. The result is a thinner assembly.

There has been speculation for most of 2013, bolstered by photos of purported iPad front and rear housings, that iPad 5 will also be narrower, with the front face adopting proportions that look similar to those of today's iPad mini.

Both sets of changes could lead to a lighter tablet, reflecting a top priority for Apple in its mobile device design.

The rumors, based on unnamed sources from companies in Apple's Asian supply chain, were repeated this week in a Wall Street Journal story.

Retina display iPad mini

The same story, and many others over the past 10 months, are the basis for the widely held conviction that Apple will reveal a high-resolution iPad mini.

Yet creating a high-res iPad mini poses a range of technical challenges. "Every device, when it goes Retina for the first time, pays a price in performance," says iMore's Rene Ritchie.

How did Apple rivals such as Google and Amazon jump to Retina-class displays on their small tablets? "Again, it's the raw pixel count that matter," says Ritchie. "1920 x 1080 (2,073,600 pixels) at ~7 hours of battery life [for Apple's rivals] is much easier than 2048 x 1536 (3,145,728) at ~10 hours of battery life [for Apple]. It requires more backlight, it requires more GPU, and it requires more power overall."

The iPad 3, the first iPad with a Retina display, was slightly heavier and thicker than iPad 2 because the Retina display required a new, much larger processor and a larger battery.

How, or whether, Apple will be able to overcome the challenges, and at least maintain current battery life for the iPad mini, remains to be seen.

Modified version of the 64-bit A7 chip

Apple surprised everyone when it introduced for iPhone 5S the first mobile 64-bit processor, the dual-core A7. A 64-bit architecture can address double the memory, a benefit for some demanding applications, but neither Apple nor its rivals are today supporting 4GB of RAM for smartphones and tablets.

But Apple is exploiting both its own processor design expertise and new features introduced in ARM Ltd's 64-bit instruction set.

KGI Securities analyst Ming-Chi Kuo, in an investors note picked up by many including MacRumors, says the iPad 5 will have a version of the A7, the "A7X" in keeping with Apple's naming conventions, while the iPad mini 2 will get the same A7 found in the iPhone 5S.

But Ritchie says the A7 for iPad mini 2 "isn't as clear." The current iPad uses the A5 chip from 2011, but the next step up, to the A6, "would rule out Touch ID [fingerprint scanner] and likely the Apple M7 [motion coprocessor] as well." It's not clear the A6 has the horsepower for Retina display; the A6X does, but it's a big component for a small space.

"Going to the Apple A7 or Apple A7X would jump two processor generations, and again shifts the question, this time to costs and production capacity on what's a brand new chipset," Ritchie says.

M7 motion coprocessor

The M7, introduced with iPhone 5S, processes a subset of information from the device's sensors such as the accelerometer, gyroscope and magnometer. This work is offloaded from the main processors to the more power-efficient co-processor, which makes it available to apps but also can use the information to make the device "more intelligent in terms of when to activate certain features and when to slow things down and conserve battery life by checking less frequently for open networks, for instance," says Ritchie.

The same set of issues that make it a fit for the iPhone make it a fit for the iPads. But, if the M7 may be tied to the 64-bit A7. If Apple sticks with an older processor for iPad mini 2, the M7 might not appear.

Touch ID fingerprint scanner

Again, the iPhone 5S innovation is the basis for speculating that the Touch ID fingerprint scanner, integrated with the home button, will appear in one or both new iPads. Generally speaking, it's been well-received by users who simply press a thumb or finger to the button to unlock their device, instead of having to enter a passcode.

Again, if the technology is dependent on the A7, it's possible that iPad 5 might have it, but iPad mini 2 might not.

Improved iSight camera

Another iPhone 5S improvement is expected to make its way into both new iPads, upgrading the iSight camera from five to eight megapixels, a larger (1.5 micron) pixel for better quality images, a slightly larger aperture at f/2.2, and two LED flashes of different colors that are adjusted by software algorithms to create the right light balance for a specific scene.

Gold and space grey

As with the iPhone 5S, many are expecting that Apple will drop the much darker slate color for the new, easier-to-annodize slate grey and possibly add a gold option for the new iPads, if Apple thinks the flashier color will work on the large products.